This invention relates generally to automatic transmissions of motor vehicles and more particularly to the required periodic maintenance of such automatic transmissions that typically involves cleaning or changing the filter and changing the automatic transmission fluid. The fluid in automatic transmissions not only serves to lubricate the transmission, but to also transfer power from the engine through the torque converter. The ability of the automatic transmission fluid to transfer power, as well as its ability to lubricate, diminishes as the fluid becomes worn due to extended use. Regular maintenance servicing of automatic transmissions is therefore very important.
In older motor vehicles, a drain plug was provided on the torque converter that permitted draining of most of the automatic transmission fluid during maintenance service. In newer motor vehicles, the drain plug previously provided on the torque converter has been eliminated. Thus, recommended maintenance service of the automatic transmissions of these late model vehicles involves removing the pan from the underside of the transmission, discarding the used fluid that is gravitationally contained within the pan (approximately 3 quarts), cleaning or changing the transmission filter or screen, replacing the pan, and adding three quarts of automatic transmission fluid through the dipstick filler tube to replenish the used fluid drained when the pan was removed. This well known method for servicing automatic transmissions results in replacing only three quarts of the total automatic transmission fluid capacity of approximately twelve quarts. Thus, nine quarts of used transmission fluid remain in the automatic transmission. The only previously known way to completely replace the fluid in automatic transmissions has been to remove the transmission from the vehicle and dismantle it, a procedure that is far to costly to be considered as a routine maintenance alternative.
It is therefore the principal object of the present invention to provide a cost effective method and apparatus for completely replacing the fluid in automatic transmissions of motor vehicles at maintenance service intervals. This and other incidental objects are accomplished in accordance with the illustrated preferred embodiment of the present invention by providing an automatic transmission fluid change apparatus having a drain pan and associated holding tank for collecting and retaining used fluid recovered from an automatic transmission. A new fluid reservoir is provided within the apparatus to contain the quantity of new fluid required for a complete change of fluid in the transmission. To accomplish a change of fluid, the transmission pan and filter are removed and new fluid is pumped from the new fluid reservoir to the transmission orifice to which the outlet tube of the filter is typically coupled. The vehicle engine is then run at idle speed to circulate the new fluid throughout the transmission, thereby forcing all used fluid out of the transmission for collection and storage within the apparatus.